1. Field of the Invention
This invention relates to the shaping of glass sheets to be laminated, and, in particular, relates to the simultaneous shaping of a pair of glass sheets having a non-rectangular outline of non-uniform curvature in plan by a combination of gravity sag bending and press bending to a complicated shape including a longitudinal bend about a transverse axis of curvature and a complicated bend containing both convex and concave elements in elevation about a longitudinal axis. The bending to such complicated shapes requires that the glass sheets be supported in precise alignment with each of the molds used to impart the different components of the complicated bend to which the glass sheets are to be shaped. Such complicated shapes are required to enable the shaped glass sheets to be mounted in a curved mounting frame forming part of an automobile body so that the curved glass forms a laminated window that merges with the shape of the curved mounting frame and the vehicle body in which it is mounted.
2. Description of Patents of Interest
U.S. Pat. No. 2,131,873 to Goodwillie shapes one or a pair of glass sheets by sag bending to conform to the upwardly facing concave shaping surface of a solid mold of continuous extent and lowering an upper solid mold of complementary convex shape against the sagged glass sheet to mechanically press the glass into a more accurate bend. The glass is shown supported throughout its entire surface on the lower mold from the time it sags to conform to the lower mold through the pressing step and during the time the bent glass sheet is removed from the hot atmosphere of the furnace. Such prolonged engagement can produce optical defects in the vision area of the bent glass.
U.S. Pat. No. 2,442,242 to Lewis heats flat glass sheets having a straight leading edge while supported on flat strips until the leading edge engages a straight rib. A pair of heated molds of complementary shape sandwich the hot glass to impress a cylindrical shape thereon. This patent is limited in its application to sheets having a straight edge.
U.S. Pat. No. 2,570,309 to Black sag bends a glass sheet by heating it while supported on an outline ring-type mold to conform to the mold by gravity sagging and then lifts the gravity sagged sheet on a lower solid pressing mold of concave elevation into pressing engagement against an upper solid pressing mold of complementary shape to complete the spherical bend. The spherically bent sheet is returned to the outline ring-type mold for support during quenching with chilling blasts of air to temper the bent sheet.
U.S. Pat. No. 3,208,839 to Nordberg press bends as many as three glass sheets to conforming shapes simultaneously using press bending exclusively for the shaping process.
U.S. Pat. No. 3,251,672 to Touvay and Lambert press bends a pair of tong-suspended glass sheets simultaneously followed by lamination. No means is provided to avoid or minimize tong marks in the glass sheets so treated.
U.S. Pat. No. 3,408,173 to Leflet discloses the bending and tempering of a glass sheet while supported on an outline mold shaped to have upwardly directed shaping surfaces curved convexly in elevation in one direction and curved concavely in elevation in another direction to impart a complicated shape to a glass sheet so that it is curved convexly in elevation in its longitudinal dimension and curved concavely in elevation in its transverse dimension. No press bending is suggested to minimize uncontrolled sag bending in the unsupported glass sheet area within the mold outline.
U.S. Pat. No. 3,453,161 to Golightly discloses bending at least two glass sheets simultaneously on an outline metal mold of skeleton type. No combination of sag bending steps with another type of bending to minimize uncontrolled sag is suggested in this patent.
U.S. Pat. No. 3,573,889 to McMaster, Kawecka and Nitschke discloses a method of fabricating a shaped, laminated windshield of tempered glass comprising press bending horizontally disposed glass sheets individually between upper and lower pressing molds to bend the glass sheet into exactly conforming shapes followed by assembling the bent glass sheets in sandwiching relation to a plastic interlayer sheet and laminating the assembly. This process is necessarily limited to fabricating laminates of relatively simple, gentle curvature containing glass sheets so thin they must be capable of flexing. Also, the process is inefficient as each glass sheet is shaped individually.
U.S. Pat. No. 3,778,244 to Nedelec bends glass sheets in a series of pneumatic steps or a combination of a pneumatic step followed by a mechanical step. The patent states that the invention allows to bend two sheets together instead of one on the same apparatus without having to change any step of the process even when the sheets have to be sharply bent. However, no specific way is disclosed in this patent how two sheets can be handled simultaneously by pneumatic handling. Only one sheet may be held by a suction device facing a major surface of a glass sheet assembly.
U.S. Pat. No. 3,904,460 to Comperatore press bends a pair of glass sheets to the slightly different configurations they require for inner and outer glass plies of a curved laminated windshield for automobiles. While this patented invention is capable of producing laminated windows of complicated curvature, the need to press bend each inner glass sheet separately from each outer glass sheet before laminating an inner glass sheet to an outer glass sheet provides an operation whose efficiency could be improved.